dsh-model-compat-guard: DSH Third-Party Model Compatibility Guard

`dsh-model-compat-guard` is a third-party model compatibility plugin designed for DeepSeek Harness (DSH). By intercepting and repairing request flows, it addresses four high-frequency issues encountered when using DSH with models such as GPT and Qwen-thinking: thinking-model compression truncation, sandbox privilege escalation request failures, missing tool descriptions, and Code Mode errors. The plugin supports flexible configuration via `~/.dsh/compat-guard.json`, works with zero configuration by default, and is suitable for developers who need stable operation of thinking models or Code Mode.